| /* |
| * Copyright (c) 2016 The WebRTC Project Authors. All rights reserved. |
| * |
| * Use of this source code is governed by a BSD-style license |
| * that can be found in the LICENSE file in the root of the source |
| * tree. An additional intellectual property rights grant can be found |
| * in the file PATENTS. All contributing project authors may |
| * be found in the AUTHORS file in the root of the source tree. |
| */ |
| |
| #ifndef WEBRTC_RTC_BASE_TIMESTAMPALIGNER_H_ |
| #define WEBRTC_RTC_BASE_TIMESTAMPALIGNER_H_ |
| |
| #include <stdint.h> |
| |
| #include "webrtc/base/constructormagic.h" |
| |
| namespace rtc { |
| |
| // The TimestampAligner class helps translating camera timestamps into |
| // the same timescale as is used by rtc::TimeMicros(). Some cameras |
| // have built in timestamping which is more accurate than reading the |
| // system clock, but using a different epoch and unknown clock drift. |
| // Frame timestamps in webrtc should use rtc::TimeMicros (system monotonic |
| // time), and this class provides a filter which lets us use the |
| // rtc::TimeMicros timescale, and at the same time take advantage of |
| // higher accuracy of the camera clock. |
| |
| // This class is not thread safe, so all calls to it must be synchronized |
| // externally. |
| class TimestampAligner { |
| public: |
| TimestampAligner(); |
| ~TimestampAligner(); |
| |
| public: |
| // Translates camera timestamps to the same timescale as is used by |
| // rtc::TimeMicros(). |camera_time_us| is assumed to be accurate, but |
| // with an unknown epoch and clock drift. |system_time_us| is |
| // time according to rtc::TimeMicros(), preferably read as soon as |
| // possible when the frame is captured. It may have poor accuracy |
| // due to poor resolution or scheduling delays. Returns the |
| // translated timestamp. |
| int64_t TranslateTimestamp(int64_t camera_time_us, int64_t system_time_us); |
| |
| protected: |
| // Update the estimated offset between camera time and system monotonic time. |
| int64_t UpdateOffset(int64_t camera_time_us, int64_t system_time_us); |
| |
| // Clip timestamp, return value is always |
| // <= |system_time_us|, and |
| // >= min(|prev_translated_time_us_| + |kMinFrameIntervalUs|, |
| // |system_time_us|). |
| int64_t ClipTimestamp(int64_t filtered_time_us, int64_t system_time_us); |
| |
| private: |
| // State for the timestamp translation. |
| int frames_seen_; |
| // Estimated offset between camera time and system monotonic time. |
| int64_t offset_us_; |
| |
| // State for the ClipTimestamp method, applied after the filter. |
| // A large negative camera clock drift tends to push translated |
| // timestamps into the future. |clip_bias_us_| is subtracted from the |
| // translated timestamps, to get them back from the future. |
| int64_t clip_bias_us_; |
| // Used to ensure that translated timestamps are monotonous. |
| int64_t prev_translated_time_us_; |
| RTC_DISALLOW_COPY_AND_ASSIGN(TimestampAligner); |
| }; |
| |
| } // namespace rtc |
| |
| #endif // WEBRTC_RTC_BASE_TIMESTAMPALIGNER_H_ |